Caliper piston bore "residue"

[paulfurn]

Hi all,

 

I'm sorry to start a new thread on this, though I couldnt find reference to this specific topic it in any of the other caliper threads.

 

Following a (fully!) seized piston on my front caliper, I decided to do a refurb, having done a refurb on the rear caliper some months ago.

 

I've spent this afternoon dismantling the caliper in prep for the parts coming tomorrow, and after _heaps_ of trouble (ending with me banging the damn thing through the fluid line hole a hole punch for about 30 minutes!) I managed to get the stuck piston out of the caliper bore/barrel. The seal was practically fused on... stuck fast!

 

However, on cleaning the caliper I noticed a stark difference inside the piston bore, as compared to the last time I did it, and also to the photo's in Bromy's (excellent) guide.

 

Bromy's piston bore is very clean and you can clearly see the silver metal inside, as it was last time I did my rear calipers.

 

However the inside of my piston bore - both bore holes - appear to be covered in some sort of brown residue. At first I thought this was rust, but some is removed with the help of a paper towel (but not much I must say.) Thats not to say it isnt rust of course, but needless to say Im a bit worried about putting a brand new piston, seal and ring (etc) as (I would imagine) its only going to foul against the rust and disintegrate the seal.

 

I'd really appreciate any input or advice, is it advisable to use some sort of rubbing paper - perhaps Emery paper (if so, what what grit is recommended.. 100 Grit okay?) - to clean, or does anyone know of off the shelf solutions that would remove it?

 

Here's a few pics:

 

http://img138.imageshack.us/img138/7530/dsc00748ds2.jpg

 

Another:

 

 

http://img91.imageshack.us/img91/3305/dsc00749sl4.jpg

 

And another:

 

http://img107.imageshack.us/img107/1836/dsc00750pe4.jpg

 

And compare them to Bromy's clean bore/piston barrel:

 

 

Thank you for any help guys

 

Paul.

Edited May 14, 2008 by paulfurn
Linked to smaller thumbnails, rather than full size pics! (see edit history)

[Andy Blyth]

With regards to getting a siezed piston out, (and I realise it may be a bit late now!) I found the easiest way to remove it was to reconnect it back up to the brake line, bleed, then pump the brake pedal till the piston is almost out of the calliper.

 

I had the same problem with my rear J Spec calliper. Tried pushing it out from the back through the hole like you did. Turns out the braking system can generate quite a pressure!

 

 

Edit to add that I used something around 300 grit wet and dry to remove some rust present between the dust seal and the piston seal. Took it back to the bare metal. The brake has been fine since.

Edited May 14, 2008 by Andy Blyth (see edit history)

[DannoSupra]

Looks to me like rust gone very very hot... as you can imagine the heat off brakes as their binding due to piston seizure... seen it before, and possibly someone has had a go at doing it before, and used copper grease, looks like a combined stain and heat

 

Just clean it up and fit the new parts bud, should be fine

[TLicense]

Just clean it out and fit new seals, it should be fine.

When you put it back together make sure you fully bleed the system with new fluid, and also check for any seepage from the piston bores past the seals.

Edited May 14, 2008 by TLicense (see edit history)

[paulfurn]

Thanks for the help guys, very much appreciated indeed!

 

Ill get cracking on the cleaning tomorrow.

 

Should I flush it completely - was just going to top up with the 2L of new fluid and bleed. To my suprise when I pumped the brake pedal to get the piston out originally only a bit of the fluid came out - when I did it with the rears it practically emptied the resevoir and pedal went to floor!) and how should I go about it (sorry, I know Im being thick but its been a long day!)

 

Thanks again!

[Chris Wilson]

Get a ball hone of the right sizing and lightly hone the bores out. A ball hone is made of carbide balls on the end of the bristles of a tiny "toilet brush" that is driven in the chuck of an air or electric drill.